Roller thrust bearing cage and manufacturing method thereof

ABSTRACT

A manufacturing method of a roller bearing cage, including a cage main body formed with an annular plate, and a plurality of cage pockets opened along a circumferential direction on the cage main body for retaining rollers having flat end faces, includes punching an annular plate from a metal, forming a plurality of cage pockets on the annular plate, and pressing an edge of one of the cage pockets in a thickness direction of the annular plate on a side face of the one of the cage pockets with a press jig having a pressing face of a predetermined shape to form a chamfered portion.

The present application is a Divisional Application of U.S. patentapplication Ser. No. 11/272,759, filed on Nov. 15, 2005, now U.S. Pat.No. 7,837,394 which is based on and claims priority from Japanese patentapplication No. 2004-331782, filed on Nov. 16, 2004, the entire contentsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to roller bearing cages such as needleroller thrust bearings etc. More specifically, the invention relates toroller bearing cages such as needle roller thrust bearings etc. that areused in an automatic transmission of automobile, a compressor of avehicle air conditioner or the like.

2. Description of the Related Art

Trend for low fuel consumption of automobile in recent years hasincreased demands for further weight saving and further reduction ofrotational torque to the roller thrust bearings that are mounted invarious parts such as automatic transmission in the vehicle more andmore. For weight saving, a cage made of resin has been proposed. Forreduction of rotational torque, there has been proposed a cage in whichprojections are formed at central parts in the circumferential directionon opposite inner faces of the cage pocket over the thickness directionof the cage (width direction of assembly) to pivotally support a rollerby contacting with circumferential central portions on end faces of theroller on inner and outer circumferential sides (See Japanese PatentPublication No. JP 2004-211824A). In the cage disclosed in JP2004-211824A, by providing the projections in opposite inner faces ofthe cage pocket, the reduction of rotational torque can be accomplishedbecause contact area between the opposite inner faces and the end facesof the roller is reduced. However, in such the cage, due to limitationin machining shape of punching die for the cage pocket, the projectionsmust extends over the thickness direction of the cage. Accordingly, alinear contact area between the projections and the end faces of theroller in the thickness direction is increased, and contact portions areexposed to a large difference in contact speeds in the thicknessdirection. As a result, in such the structure, abnormal wear (drillingwear) can easily occur on the inner faces of the cage pocket. As thecage disclosed in JP 2004-211824A is made of metal, the thickness of thecage can be made relatively thin, so that the length of the linearcontact of the projection can be made small. However, if the cage ismade of resin for saving weight, the thickness of the cage is increasedin order to secure strength of the cage and also, due to limitation inshape to provide draft for releasing resin formation mold, theprojection must be made to extend more in the thickness direction of thecage as compared with the metal cage. Accordingly, the difference in thecontact speeds between the projection and the end face of the roller isfurther increased, and the drilling wear as discussed above becomes moreconsiderable.

SUMMARY OF THE INVENTION

One of the problems to be solved in the present invention is to obtainweight saving and reduction in rotational torque in a roller thrustbearing while suppressing drilling wear as described foregoing in eithercases that the cage is made of metal or resin. In particular, in a casethat the thickness of the cage must be large because the cage is made ofresin, or the like, the invention provides a roller bearing cage thatcan contribute to further weight saving and reduction in rotationaltorque of the roller bearing while having significant effect onsuppressing the drilling wear.

The invention provides a roller bearing cage that includes a cage mainbody formed with an annular plate, and a plurality of cage pocketsopened so as to be arranged along a circumferential direction on thecage main body for retaining rollers having flat end faces;

wherein a projection to pivotally support an end face of thecorresponding roller is projected at a central portion in thecircumferential direction on a radial inner face of each cage pocket,

the projection extends in a thickness direction of the cage main body,and includes a contact portion that is brought into a contact with acentral portion or a vicinity thereof on the end face of the roller, anda non-contact portion that is adjacent to the contact portion in thethickness direction and that is not brought into contact with the endface of the roller.

In the cage according to the invention, in order to secure large loadcapacity to the roller seated in the cage pocket, the roller having flatend faces is retained, and in order to reduce frictional resistance bycontact between the inner faces of the cage pocket and the end faces ofthe roller, a projection is formed at least at the circumferentialcentral part on the inner face of the cage pocket (namely,circumferential side face of the cage pocket). The projection has ashape extending in the thickness direction to secure draft for releasingthe cage from the formation mold. More specifically, the projectionextends in the thickness direction at the circumferential centralportion and a flat portion formed in the central part of the projectionlinearly extends in the thickness direction. By such the structure, ifnon-contact portion is not formed, the contact area between theprojection on the inner face of the cage pocket and the end face of theroller would be formed linearly in the thickness direction causingcircumferential speed difference. In such a state, a drilling wear caneasily occur.

Under foregoing circumstances, according to the invention, theprojection includes a contact portion that is brought into a contactwith a central portion or a vicinity thereof on the end face of theroller, and a non-contact portion that is adjacent to the contactportion in the thickness direction and that is not brought into contactwith the end face of the roller. Therefore, the projection is configuredto reduce the contact area between the projection and the roller endface. As a result, according to the invention, the drilling wear due tothe liner contact between the inner face of the cage pocket and theroller end face is reduced and it is possible to obtain a reduction inrotational torque. Further, according to the invention, in a case thatthe cage is made of resin for weight saving, even if the cage thicknessis made thick to secure the cage strength and the projection is madelong in the thickness direction of the cage, only the contact portionformed in a part of the projection is brought into linear contact withthe roller end face. Accordingly it is possible to reduce or suppressthe drilling wear and to obtain simultaneously the weight saving andreduction in rotational torque of the bearing in which the cage of theinvention is mounted for low fuel consumption of an automobile.

Further, in a case that a semi-circle projection is formed on the innerface of the cage pocket to pivotally support the central portion on theroller end face by almost point contact, the difference in thecircumferential speeds does not occur at the contact area between theprojection and the roller end face. However, if the cage is moved in thethickness direction thereof, the projection and the central portion onthe roller end face are offset to each other and non-contacttherebetween occurs and the projection cannot pivotally support theroller. On the other hand, according to the invention, the flat portionmay have a flat length that is at least almost equivalent to adisplaceable distance of the cage in the thickness direction. By suchthe construction, even if the cage is moved in the thickness direction,the contact portion assuredly keeps a state that the contact portion isalways brought into contact with the central portion on the roller endface, so that the roller in motion is pivotally supported and its smoothrotational motion is maintained.

The non-contact portion may include a chamfered portion formed on anedge of the projection in the thickness direction of the cage. Thecontact portion may include a flat portion having a flat face in thethickness direction of the cage in a central part of the projection. Apair of the chamfered portions may be formed on the opposite edges ofthe projection in the thickness direction of the cage.

The cage of the invention may be a needle roller bearing cage or aroller bearing cage other than needle roller bearing. The cage of theinvention does not limit type of the bearing to which the cage isapplied as far as the bearing is provided with a cage. The cage may bemade of resin or may be made of metal. If the cage is made of resin, thethickness of the cage becomes relatively large. Therefore, the inventionis specifically suitable for sufficiently suppressing the drilling wearin such the resin cage. If the cage is made of metal, although the cagethickness is relatively small, the invention is also suitable forsuppressing the drilling wear by providing the non-contact portion in apart of the projection.

Second aspect of the invention is provided with a manufacturing methodof a roller bearing cage including a cage main body formed with anannular plate, and a plurality of cage pockets opened so as to bearranged along a circumferential direction on the cage main body forretaining rollers having flat end faces, including punching an annularplate from a metal, forming a plurality of cage pockets on the annularplate, and pressing an edge of one of the cage pockets in a thicknessdirection of the annular plate on a side face of the cage pocket with apress jig having a pressing face of a predetermined shape to form achamfered portion.

By such a manufacturing method of a roller bearing cage, a cage havingthe above-described construction and advantages can be obtained.

According to the invention, the drilling wear due to a contact betweenthe inner face of the cage pocket and the roller end face is reduced andit is possible to obtain weight saving and reduction in rotationaltorque in the cage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial plan view showing a roller bearing cage according toEmbodiment 1;

FIG. 2 is an enlarged plan view showing a vicinity of a cage pocket inFIG. 1;

FIG. 3 is a sectional view taken on line of FIG. 2;

FIG. 4 is an explanatory view showing a displaceable amount in thethickness direction of the cage;

FIG. 5 is a partial plan view showing a roller bearing cage according toEmbodiment 2;

FIG. 6 is an enlarged plan view showing a vicinity of a cage pocket inFIG. 5;

FIG. 7 is a sectional view taken on line VII-VII of FIG. 6; and

FIGS. 8A through 8C show a process forming chamfered portions of thecage of FIG. 5, and FIG. 8D shows a modification of the process formingthe chamfered portions of the cage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the description will be made on the rollerbearing cages according to the embodiments of the invention. Althoughthe roller bearing cages of the embodiments are applied to needle rollerbearing cages, the invention is applicable other types of roller bearingcages.

(Embodiment 1)

FIGS. 1 through 4 show the cage of Embodiment 1. FIG. 1 is a partialplan view showing a roller bearing cage, FIG. 2 is an enlarged plan viewshowing a vicinity of a cage pocket in FIG. 1, FIG. 3 is a sectionalview taken on line of FIG. 2, and FIG. 4 is an explanatory view showinga displaceable amount in a thickness direction of the cage.

A cage 10 according to Embodiment 1 as shown in FIG. 1 includes a ringplate 11 having an annular shape and formed of a resin, on which cagepockets 12 for retaining rollers are formed at plural positions alongcircumferential direction. The cage pockets 12 are opened and arrangedin a radial manner around the center of the cage at a constant pitch ofa predetermined angle. Each cage pocket 12 is formed in a rectangularshape elongated slightly in the radial direction from the center of thecage in accordance with the roller length, and houses a roller 13 havingflat end faces to obtain a large load capacity. Resin material for thering plate 11 is not specifically limited if it is suitable in terms ofthe cage performance and cage strength etc. For example, the cage may beconstituted by a material in which polyamide 66, polyamide 46,polyphenylene sulfide, thermoplastic polyimide or the like is served asmatrix, and glass fiber, carbon fiber, aramid fiber or the like may beadded in the matrix to improve the strength. Polyamide 66 isparticularly suitable for material of the cage because it has excellentproperties such as tensile strength and bending stiffness and has smallcoefficient of linear expansion.

A roller retaining portion (not-shown) for preventing the roller 13 fromrunning off on a circumferential inner face 12 a of the cage pocket 12.Projections 14 are formed on opposite radial inner faces 12 a to reducefrictional resistance by contact between the inner faces 12 a and endfaces 13 a of the roller 13.

Embodiment 1 is generally characterized by the shape of the projections14. Referring to FIGS. 2 and 3, the shape of one of the projections 14will be described in detail below. The projection 14 has a shapeprojecting into the cage pocket 12 at a central part in thecircumferential direction on the inner surface 12 a of the cage pocket12 over a thickness direction (height direction) of the cage 10. Theprojection 14 has a curved surface shape such as semi-circle orsemi-ellipse, so that the projection 14 is brought into a point contactwith a circumferential central portion 13 b on the roller end face 13 a.The projection 14 extends in the thickness direction of the cage 10between opposite edges of the inner surface 12 a of the cage pocket 12.Opposite edges of the projection 14 are chamfered, so that a sectionalshape of the projection 14 is constituted by chamfered portions(non-contact portions) 14 a on the opposite edges and a flat portion(contact portion) 14 b in the center part. In other words, the chamferedportions 14 a are formed adjacent to the flat portion 14 b in thethickness direction. Sectional shape of the chamfered portions 14 a isnot limited to straight, and it may be formed with a curved shape suchas rounded shape. Chamfering angle of the chamfered portions 14 a is notspecifically limited. In a case that the cage 10 is formed by aconventional method such as injection molding, the opposite edges of theprojection 14 may be formed in chamfered shapes serving as draft.Therefore, the cage 10 after formed can be easily drawn from the resinformation mold. The chamfered portions 14 a of the projection 14 formnon-contact portions that do not contact with the end face 13 a of theroller 13. Although the non-contact portions are formed in a chamferedshape (rounded or tapered shape) in Embodiment 1, the non-contactportions may include a shape formed in a stepped manner with respect tothe flat portion 14 b. The non-contact portions may have a shape so asnot to contact with the end face 13 a of the roller 13, however, theshape of the chamfered portions 14 a is preferable to serve as draft forbeing released from the mold after resin formation. By adjusting thechamfering angle of the chamfered portions 14 a, a preferable draft forbeing released from the mold can be obtained.

The flat portion 14 b constitutes a maximum projected part of theprojection 14 into the cage pocket 12 so as to pivotally support theroller 13 which is seated in the cage pocket 12 by contacting with acentral portion 13 c in the thickness direction of the cage 10 on theend face 13 a of the roller 13. The flat portion 14 b of the projection14 constitutes a contact portion that is brought into contact with aregion including the central portion 13 c on the end face 13 a of theroller 13 so as to be in parallel with each other. Although the shape ofthe contact portion is constituted by a shape that is flat and inparallel with the end face 13 a of the roller 13 in Embodiment 1, thecontact portion may contain a slightly rounded shape at boundaries tothe chamfered portions 14 a so as to form continuity therebetween. It ispreferable to avoid unnecessary frictional contact with the end face 13a of the roller 13 at the boundaries by forming continuity in shapechange between the flat portion 14 b and the chamfered portions 14 a.

Referring to FIG. 4, the flat portion 14 b is described more indetailed. In a case that the cage 10 of Embodiment 1 is mounted betweenan outer peripheral housing member and an inner peripheral side shaftmember as a roller thrust bearing without race ring or a roller thrustbearing with race ring, it is assumed that the cage 10 is displaceableat a distance LO in the thickness direction. In other words, the cage 10is displaceable up to a first displacement position P1 shown with chainline on one side in the thickness direction, on the other hand, the cage10 is displaceable up to a second displacement position P2 shown withchain double dashed line on the other side in the thickness direction.The distance between the positions P1 and P2 makes L0. The flat portion14 b has a flat length L1 that is at least almost equivalent to theabove-described displaceable distance L0 in the thickness direction ofthe cage 10. Preferably, the flat portion 14 b has a flat length L1 thatis slightly longer than the above-described displaceable distance L0 inthe thickness direction of the cage 10. Preferably, the flat length L1of the flat portion 14 b should be made as short as possible, so as toreduce frictional resistance by contact to the roller end face 13 a andto reduce difference in circumferential speeds at the contact portionbetween the flat portion 14 b and the roller end face 13 a. In a casethat the cage 10 is not displaced in the thickness direction, the flatlength of the flat portion 14 b should be made with a small length closeto zero preferably. Namely, the projection 14 is preferably brought intoalmost point contact, while not pure point contact, to the centralportion 13 c in the thickness direction of the cage 10 on the end face13 a of the roller 13. However, the cage 10 is normally displaced in thethickness direction, the flat length L1 of the flat portion 14 b is madealmost equivalent to the displaceable distance L0 of the cage 10 in thethickness direction thereof in Embodiment 1.

Accordingly, in the cage 10 of Embodiment 1, in a case that the cage 10is displaced to the first displacement position P1 on one side in thethickness direction, an end of the flat portion 14 b of the projection14 that is located on the other side in the thickness directioncorresponds to the central portion 13 c in the thickness direction onthe roller end face 13 a, whereas, in a case that the cage 10 isdisplaced to the second displacement position P2 on the other side inthe thickness direction, another end of the flat portion 14 b of theprojection 14 that is located on one side in the thickness directioncorresponds to the central portion 13 c in the thickness direction onthe roller end face 13 a. As a result, the flat portion 14 c can be incontact with the central portion 13 c in the thickness direction on theroller end face 13 a in any case that the cage 10 is displaced at anyposition in the thickness direction. Hence, the flat portion 14 bassuredly keeps a state that the flat portion 147 b is always broughtinto contact with the central portion 13 c in the thickness direction onthe roller end face 13 a, so that the roller 13 in motion is pivotallysupported and its smooth rotational motion is maintained.

In the cage 10 having the above described construction, the flat portion14 b to contact with the central portion 13 c of the roller end face 13a at a part of the projection 14 and the flat length of the flat portion14 b is formed to as to be at least almost equivalent to thedisplaceable distance in the thickness direction of the cage 10. Henceonly the part of the projection 14 is brought into linear contact withthe central portion 13 c in the thickness direction of the cage 10 onthe roller end face 13 a, so that a drilling wear is much reduced byreducing the area of the linear contact.

Further, in the cage 10, even if the cage 10 is made of resin and itsthickness becomes relatively large, only the flat portion 14 b that isthe part of the projection 14 is brought into linear contact with theroller end face 13 a. Hence, the drilling wear is suppressed and it ispossible to reduce a rotational torque to be required.

(Embodiment 2)

FIGS. 5 through 8D show the cage according to Embodiment 2. FIG. 5 is aplan view showing a roller bearing cage, FIG. 6 is an enlarged plan viewshowing a vicinity of a cage pocket in FIG. 5, FIG. 7 is a sectionalview taken on line VII-VII of FIG. 6, FIGS. 8A through 8C show a processforming chamfered portions of the cage of FIG. 5, and FIG. 8D shows amodification of the process forming the chamfered portions of the cage.

Referring to FIGS. 5 through 7, the cage 10 shown in these drawingsincludes a ring plate 11 formed from a metal like light alloy etc. or asteel plate by punching. The ring plate 11 has a W-shaped section in theradial direction and plurality of roller retaining cage pockets 12 areformed in a radial manner around the center of the cage 10. The cagepockets 12 are opened and formed simultaneously at the forming of thering plate 11 by punching. Further, a roller retaining portion 12 b isformed on a circumferential inner face 12 a. On a radial inner face 12a, a projection 14 is formed similarly to Embodiment 1.

Similarly to Embodiment 1, the projection 14 has a shape projecting intothe cage pocket 12 at a central part in the circumferential direction onthe inner surface 12 a of the cage pocket 12 over a thickness directionof the cage 10. Opposite edges of the projection 14 in the thicknessdirection are chamfered, so that a sectional shape of the projection 14is constituted by chamfered portions (non-contact portions) 14 a on theopposite edges and a flat portion (contact portion) 14 b that is flat inthe thickness direction. The flat portion 14 b is constituted topivotally support a roller 13 which is seated in the cage pocket 12 bycontacting with a central portion 13 c in the thickness direction on anend face 13 a of the roller 13.

The flat portion 14 b of the projection 14 has a flat length L1 that isat least almost equivalent to a displaceable distance LO in thethickness direction of the cage 10. Accordingly, in a case that the cage10 is displaced to the first displacement position on one side in thethickness direction, or in a case that the cage 10 is displaced to thesecond displacement position on the other side in the thicknessdirection, the flat portion 14 b corresponds to the central portion 13 cin the thickness direction on the roller end face 13 a. As a result, theflat portion 14 c can be in contact with the central portion 13 c in thethickness direction on the roller end face 13 a in any case that thecage 10 is displaced at any position in the thickness direction.

In the cage 10 according to the above-described Embodiment 2, similarlyto Embodiment 1, only the part of the projection 14 is brought intolinear contact with the central portion 13 c in the thickness directionof the cage 10 on the roller end face 13 a, so that a drilling wear ismuch reduced by reducing the area of the linear contact.

The chamfered portions 14 a may be formed by pressing an radial innerface of the cage pocket 12 formed by punching with an annular press jig15 that is provided with a pressing face 15 a having an anglecorresponding to an chamfering angle of the chamfered portions 14 a. Inother words, as shown in FIG. 8A, the cage 10 and the press jig 15 aredisposed in an opposite manner, and then opposite edges of theprojection 14 in the thickness direction of the cage 10 are pressed withthe press jig 15. Thus, the chamfered portions 14 a are formed on theopposite edges of the projection 14 of the cage 10 as shown in FIG. 8C.The flat portion 14 b is formed simultaneously to the formation of thechamfered portions 14 a.

Incidentally, as shown in FIG. 8D, a pair of the press jigs 15 may bedisposed in an opposite manner interposing the cage 10, and the oppositeedges of the projection 14 in the thickness direction may besimultaneously pressed with the press jigs 15, so that the chamferedportions 14 a and the flat portion 14 b are simultaneously formed.

The invention is not limited by the foregoing embodiments. The inventionshould include various changes or modification within the scope of theclaims.

What is claimed is:
 1. A manufacturing method of a roller bearing cageincluding a cage main body formed with an annular plate, a plurality ofcage pockets opened on the cage main body so as to be aligned along acircumferential direction of the annular plate, and the cage pocketsconfigured to accommodate rollers having flat end faces, said methodcomprising: punching a metallic plate in an axial direction of themetallic plate; forming a plurality of cage pockets opened on the faceof the annular plate; and pressing an edge of one of the cage pockets ina thickness direction of the annular plate with a press jig to form achamfered portion and a flat portion on a side face of the one of thecage pockets, in a cross sectional view, the edge extending orthogonalto the radial direction so as to oppose one of the flat end faces of therollers, wherein the press jig comprises a pressing face of apredetermined shape to form the chamfered portion, wherein the flatportion extends in the thickness direction, in a central part of theside face of the one of the cage pockets in the thickness direction, andwherein the chamfered portion is inclined to both of the radialdirection and the thickness direction.
 2. The manufacturing method of aroller bearing cage according to claim 1, wherein the cage pockets aresimultaneously formed at the punching of the annular plate from themetal.
 3. The manufacturing method of a roller bearing cage according toclaim 1, wherein the flat portion is formed simultaneously at theforming of the chamfered portion by the pressing the edge of the one ofthe cage pockets in the thickness direction on the side face of the oneof the cage pockets with the press jig.
 4. The manufacturing method of aroller bearing cage according to claim 1, wherein opposite edges of theone of the cage pockets in the thickness direction are simultaneouslypressed with a pair of press jigs, so that the flat portion and a pairof said chamfered portion adjacent to the flat portion aresimultaneously formed.
 5. The manufacturing method of a roller bearingcage according to claim 1, further comprising: forming another chamferedportion adjacent to the flat portion by the pressing the edge of the oneof the cage pockets in the thickness direction on the side face of thecage pocket.
 6. The manufacturing method of a roller bearing cageaccording to claim 5, wherein the flat portion is formed adjacent to thechamfered portion.
 7. The manufacturing method of a roller bearing cageaccording to claim 5, wherein a length of the flat portion is at leastequivalent to a displaceable distance in a thickness direction of thecage main body, said displaceable distance being defined as a distancethat the roller bearing cage is displaced when the roller bearing cageis mounted between an outer peripheral housing member and an innerperipheral side shaft member.
 8. The manufacturing method of a rollerbearing cage according to claim 1, wherein the flat portion is formedadjacent to the chamfered portion simultaneously at the forming of thechamfered portion.
 9. The manufacturing method of a roller bearing cageaccording to claim 1, wherein the flat portion is formed adjacent to thechamfered portion such that a length of the flat portion is at leastequivalent to a displaceable distance in a thickness direction of thecage main body, said displaceable distance being defined as a distancethat the roller bearing cage is displaced when the roller bearing cageis mounted between an outer peripheral housing member and an innerperipheral side shaft member.
 10. The manufacturing method of a rollerbearing cage according to claim 1, wherein the flat portion extendslinearly in the thickness direction on the side face.
 11. Themanufacturing method of a roller bearing cage according to claim 1,further comprising pressing another edge of the one of the cage pocketsto form another chamfered portion, said another chamfered portion andsaid chamfered portion forming a pair of chamfered portions, wherein theflat portion is formed between the pair of said chamfered portions. 12.The manufacturing method of a roller bearing cage according to claim 11,wherein the pair of said chamfered portions is formed symmetrical andadjacent to the flat portion.
 13. The manufacturing method of a rollerbearing cage according to claim 11, wherein, in the radial direction ofthe annular plate, the flat portion protrudes on the side face of theone of the cage pockets more than the pair of said chamfered portions.14. The manufacturing method of a roller bearing cage according to claim11, wherein, in the radial direction of the annular plate, the flatportion protrudes on the side face of the one of the cage pockets morethan other portions of the side face of the one of the cage pockets. 15.The manufacturing method of a roller bearing cage according to claim 1,further comprising pressing another edge of the one of the cage pocketsto form another chamfered portion, said another chamfered portion andsaid chamfered portion forming a pair of chamfered portions, wherein thepair of said chamfered portions is formed symmetrical with respect tothe flat portion.
 16. The manufacturing method of a roller bearing cageaccording to claim 1, further comprising pressing another edge of theone of the cage pockets to form another chamfered portion that extendswith an inclined angle from an edge of the flat portion.
 17. Themanufacturing method of a roller bearing cage according to claim 15,wherein, in the cross sectional view, the flat portion is located in acentral portion of the edge of said one of the cage pockets, and thechamfered portion and said another chamfered portion are located insides of the central portion of the edge of said one of the cagepockets.
 18. The manufacturing method of a roller bearing cage accordingto claim 15, wherein, in the cross sectional view, the flat portion islocated in a central portion of the edge of said one of the cagepockets, and the chamfered portion and said another chamfered portionextend symmetrically with respect to the flat portion from edges of thecentral portion.
 19. The manufacturing method of a roller bearing cageaccording to claim 16, wherein, in the cross sectional view, the flatportion is located in a central portion of the edge of said one of thecage pockets, and the chamfered portion and said another chamferedportion extend from edges of the central portion of the edge of said oneof the cage pockets.
 20. The manufacturing method of a roller bearingcage according to claim 16, wherein, in the cross sectional view, theflat portion is located in a central portion of the edge of said one ofthe cage pockets, and the chamfered portion and said another chamferedportion extend symmetrically with respect to the flat portion from edgesof the central portion.